The present invention relates to the field of autoalignment systems for high power lasers and more particularly to autoalignment systems utilizing output beam sampling by means of diffractive reflection gratings. In even greater particularity, the present invention relates to autoalignment systems capable of compensating for the thermal distortion of a beam-sampling reflection grating.
In many potential high power laser applications it is necessary to control the direction of output beam propagation to within a few micro-radians. Consequently, the development of highly accurate autoalignment systems for such lasers is of current interest. Methods suggested for approaching this alignment problem include using a low-power, usually HeNe, alignment laser beam propagating along the high-power laser train and direct optical sampling of the high-power output beam. The latter method must resolve an initial design problem; standard optical sampling techniques, such as beam splitting, are infeasible due to the extremely high power levels involved. A beam sampling technique which has been suggested for these high power levels is the use of a diffractive reflection grating. However, thermal distortions occurring in close-line-spacing, linear reflection gratings produce errors in the angle of the diffracted beam which limit the usefulness of the grating as a beam sampler in highpower applications. While work has been done on improving the thermal properties of reflection gratings, distortion problems still exist. In addition, it is not clear that the continued improvement of reflection gratings is the most cost effective way to facilitate the use of these gratings in high power laser applications.